This invention relates to a molded carpet assembly suitable for use in automobiles. The carpeting used to cover the floor areas of automobiles is conventionally molded into a nonplanar three dimensional contoured configuration which conforms to the contours of the automobile floor so as to fit properly, for example, over the transmission hump on the floor of the automobile. In order to make the carpeting moldable and shape sustaining, it is conventionally provided with a backing or coating of a thermoplastic polymer composition. The thermoplastic polymer backing may contain substantial amounts of inorganic fillers to improve the sound deadening properties of the carpet assembly. Additionally, the automotive carpets are normally provided with padding on the rear surface for cushioning, sound deadening, and thermal insulation. The pads are commonly formed from relatively inexpensive fibers such as jute or recycled waste fibers, and they are precut into predetermined desired shapes and bonded to the back coated surface of the molded carpet.
In the production of this type of molded carpet assembly, a number of difficulties have been encountered. The fiber pads often vary in size and thickness, which results in nonuniformity of the resulting product. This construction requires manual placement and assembly of the pads which, in addition to the labor costs involved, often results in variations in placement of the pads on the carpet backing, which further contributes to a nonuniform product and results in a poor fit when the carpet assembly is later installed in the automobile. Difficulties are also encountered in obtaining good adherence between the fiber waste pads and the carpet backing. As a result, the pads may have a tendency to become detached during subsequent handling or installation.
The aforementioned commonly-owned copending application provides an improved molded carpet assembly which avoids the necessity of using precut fiber pads which must be properly placed and secured to the carpet backing, and instead provides foam pads which are formed in situ at the desired locations on the back of the molded carpet assembly. This type of carpet assembly provides significant advantages over the fiber pad backed carpets of the prior art. For example, it is possible to achieve much more precise control over the thickness, size and placement of the foam pads and to thereby obtain a better fit and conformance of the carpet assembly to the floor of the automobile.
The present invention provides further improvements in a molded foam-backed carpet assembly of the general type disclosed and claimed in the aforementioned copending application. More particularly, in accordance with the present invention there is provided a molded foam-backed automobile carpet assembly which is designed to provide enhanced sound deadening properties to the carpet assembly. It has been found that through careful selection and control over the characteristics of the foam backing, the vibration damping characteristics and hence the overall acoustical sound deadening properties of the carpet assembly can be significantly improved.
Furthermore, the present invention provides an improved foam-backed carpet assembly having excellent acoustical properties with minimum weight. Prior to the present invention, the prevalent understanding was that it is necessary to increase the mass of the sound insulation in order to achieve better acoustics, and typically the efforts to enhance the acoustical properties of automotive carpets have involved increasing the mass. For this purpose, a highly filled thermoplastic polymer "mass backing" layer is conventionally provided in automotive carpet assemblies. In accordance with the present invention, it has been found that through appropriate selection and control over the properties of the foam backing and of the thermoplastic polymer layer, it is possible to achieve comparable or even better acoustical properties with a reduction in overall weight.
To use foam as a pad or cushion on the back of molded automotive carpets has been previously proposed, as taught for example in various prior patents such as U.S. Pat. Nos. 4,016,318; 4,078,100, 4,186,230; 4,230,755; and DE No. 2924197, and JA No. 59/001230. However, these prior patents do not address the acoustical properties of the carpet, nor do they recognize or teach how the acoustical properties may be improved through control over the physical properties of the foam. Published U.K. patent application GB No. 2,138,012 proposes using as a sound insulation layer in an automotive carpet a polyurethane foam which has been specially formulated so as to have viscoelastic properties. Although viscoelastic foam may perform acceptably for sound insulating purposes, its lack of resilience and other physical properties make it undesirable for use as a cushioning layer under a carpet. Also, viscoelastic foams, by nature, are highly temperature dependent and therefore perform poorly under the widely varying temperature conditions encountered in an automobile.